Internal combustion engines come in a number of forms, the most common of which are spark-ignited gasoline fueled engines and compression-ignition, diesel-fueled engines. The compression-ignition, or diesel-type engine is used in many commercial and industrial power applications because its durability and fuel economy are superior to the spark-ignited gasoline-fueled engines. A diesel engine utilizes the heat of the compression of the intake air, into which a timed and metered quantity of fuel is injected, to produce combustion. The nature of the diesel engine cycle is that it has a variable air-fuel ratio that can, under partial power conditions, rise to levels significantly above stoichiometric. This results in enhanced fuel economy since only the quantity of fuel needed for a particular power level is supplied to the engine.
One of the issues with a diesel-type engine is the impact on emissions. In addition to the generation of carbon monoxide and nitrous oxide, there is a generation of particulates in the form of soot. A number of approaches are employed to reduce particulates while, at the same time, reducing oxides of nitrogen to ever more stringent levels as mandated by government regulations. Stoichiometric engines have been proposed to achieve this balance since they enable the use of an automotive type catalyst to reduce oxides of nitrogen. By operating the engine at or near stoichiometric conditions, a three-way catalyst may be utilized. However, operation in this manner causes a substantial increase in diesel particulates. Accordingly, a particulate filter (PF) in the form of a diesel particulate filter (DPF) must be employed to filter out the particulates, but the generation of particulates in a significant amount require that frequent regeneration of the filters, through temporary heating or other means, is necessary to remove the collected particulate matter. A wall-flow DPF will often remove 85% or more of the soot during operation. Cleaning the DPF includes utilizing a method to burn off the accumulated particulate either through the use of a catalyst or through an active technology, such as a fuel-burner, which heats the DPF to a level in which the soot will combust. This may be accomplished by an engine modification which causes the exhaust gasses to rise to the appropriate temperature. This, or other methods, known as filter regeneration, is utilized repeatedly over the life of the filter. One item that limits the life of the DPF is an accumulation of ash therein that will cause the filter to require replacement or some other servicing, such as a cleaning method, to remove the accumulated ash. The accumulated ash causes a reduction in the efficiency of the DPF and causes increased back pressure in the exhaust system of the diesel engine system.
U.S. Patent Application Pub. No. US 2007/0251214 discloses an apparatus for detecting a state of a DPF with a differential pressure sensor. An electronic control unit estimates an amount of ash remaining in the DPF based on the output of the differential pressure sensor immediately after the regeneration process. Alternatively, the residue ash amount may be calculated based on the difference between a ratio of the variation rate of the input manifold pressure with the variation rate of the differential pressure immediately after the regeneration process and an equivalent ratio regarding a thoroughly new or almost new diesel particulate filter. The residue ash amount is calculated every time a regeneration process is carried out and stored in memory. This method is problematic since the backpressure assessment after regeneration can be misleading if the soot has not been entirely removed and since the backpressure due to the ash accumulation measured after each regeneration can vary leading to misleading assumptions about the ash content.
U.S. Pat. No. 6,622,480 discloses a DPF unit and regeneration control method that adjusts the start timing of a regeneration operation. The method includes an estimate of the ash accumulated quantity that is in the exhaust gas and accumulated in the filter and the correction of the exhaust pressure judgment value for judging the regeneration operation start based on the ash accumulated estimation value. The ash quantity is determined from the quantity of lubricant oil consumed according to the engine operation state. The effective accumulation in the filter with ash is reflected in the judgment of regeneration start timing because the exhaust pressure judgment value to be used for judging the regeneration operation start is corrected with the ash accumulation estimation value. The use of oil consumption is problematic since the lubricant oil may be consumed in ways other than being combusted. Further, even if the oil is not combusted, it is not necessarily passed through the DPF.
It is also possible that direct-injected gasoline engines may require the use of a PF in the future, as a result of ever increasing governmental emissions standards.
What is needed in the art is a system that maximizes the life of a PF, such as a DPF, while ensuring that the regeneration process is done in an efficient, economical manner.